This invention relates to a voice controlled musical instrument in which a new output tone signal can be produced thereby from a monophonic melody input signal of audio frequency, such as an input signal created by a vocal tone sung by a man, a sound played by a musical instrument or a musical tone signal of any of audio apparatus, and more particularly to a novel voice keying system for a voice controlled musical instrument, in which any input signal is converted to an output tone signal having a smaller rate of frequency increment than the input signal has, or having a constant frequency in each of differently predetermined frequency bands, so that an output tone signal having stable and accurate frequency is produced from an input signal having unstable and inaccurate frequency.
There have heretofore been proposed some types of voice controlled musical instruments, in which an input signal is converted to a fundamental frequency signal having the frequency proportional to that of the input signal. The fundamental frequency signal is multiplied and/or divided in frequency so as to generate a plurality of octavely related tone signals. The octavely related tone signals are controlled in amplitude envelope in relation to the amplitude envelope of the input signal. Thus, a new output tone signal is produced.
In general because a pitch or interval of a vocal tone sung by a man is inaccurate and unstable, a frequency fluctuation and/or a frequency error of .+-. 1 to 2% is inevitable in a vocal tone sung by a man even if he carefully sings.
Such a frequency error or frequency fluctuation can hardly be perceived by any one when the vocal tone is heard directly. However, the frequency error or frequency fluctuation of the output tone signal can be distinctly perceived by any one when he hears a vocal tone processed by a conventional voice controlled musical instrument. Therefore, any music processed by such conventional voice controlled musical instrument is heard poorly against the player's will even if he performs skillfully. Consequently, it is very difficult for a beginner to play such a conventional voice controlled musical instrument and he is required to do many exercises to play it skillfully.